ABSTRACT: Control of the Last Glacioeustatic Change on the Organic Sedimentation in the Makassar Strait

A. Y. Huc, F. Vandenbroucke, J. Gayet

Five cores collected along a transect off the Mahakam River, during the Misedor II cruise, have been considered in this study. The fine cores are related to the shelf, slope, rise, and abyssal plain, respectively, in the Makassar strait between Kalimantan and Sulawesi.

The sediments deposited along this transect were supplied by the Mahakam river and the associated organic matter. Concentrated plant detritus and dispersed organic matter is derived mainly from the continent (type III organic matter). Late Quarternary climatic phases, including the last glaciation (Wurm), the post-glacial period, and the Holocene, have been recognized on the basis of fossil assemblages, ^dgr¹⁸O isotopes, comparison with data from Sulu sea lithostratigraphic correlations and ¹⁴C datation of plant detritus.

The higher content of plant macrodetritus in sediments deposited during the ice age and their decreasing abundance in the subsequent sediments can be rationalized in terms of glacioeustatic changes.

During the Wurm, the largest part of the continental shelf was exposed. Organic-bearing fluvial and deltaic sediments were deposited on the platform by the Mahakam River, but a part of the organic matter was conveyed toward the abyssal plain where it accumulated together with high-energy turbidites.

During the post-glacial time, rising of the sea level tended to trap a part of the fluvial sediments, including organic matter at the edge of the shelf, feeding turbidites that become finer and organically poorer as the transgression proceeds.

At present, most of the organic stock accumulates on the delta and the recent sediments deposited offshore are organically lean and influenced by hemipelagic and pelagic processes.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990